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Kubernetes_deployments

Chapter 20: Kubernetes Deployments

Section titled “Chapter 20: Kubernetes Deployments”

Deployments provide declarative updates for Pods and ReplicaSets. They manage the lifecycle of applications including rolling updates and rollbacks.

What is a Deployment?

Section titled “What is a Deployment?”
┌─────────────────────────────────────────────────────────────────────────────┐
│                        Kubernetes Deployment                                 │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                             │
│   Deployment                                                                │
│   ┌──────────────────────────────────────────────────────────────────┐   │
│   │                                                                   │   │
│   │  ┌──────────────────────────────────────────────────────────┐   │   │
│   │  │                    ReplicaSet                            │   │   │
│   │  │    ┌─────────┐   ┌─────────┐   ┌─────────┐            │   │   │
│   │  │    │  Pod 1   │   │  Pod 2   │   │  Pod 3   │            │   │   │
│   │  │    │ nginx:1.2│   │ nginx:1.2│   │ nginx:1.2│            │   │   │
│   │  │    └─────────┘   └─────────┘   └─────────┘            │   │   │
│   │  └──────────────────────────────────────────────────────────┘   │   │
│   │                                                                   │   │
│   └──────────────────────────────────────────────────────────────────┘   │
│                                                                             │
│   Benefits:                                                                │
│   ✓ Declare desired state                                                 │
│   ✓ Rolling updates                                                       │
│   ✓ Rollback to previous versions                                         │
│   ✓ Scale up/down                                                          │
│   ✓ Self-healing                                                          │
│                                                                             │
└─────────────────────────────────────────────────────────────────────────────┘

Creating Deployments

Section titled “Creating Deployments”

Using kubectl

Section titled “Using kubectl”
Terminal window
# Create deployment
kubectl create deployment nginx --image=nginx:latest


# Create with replicas
kubectl create deployment nginx --image=nginx:latest --replicas=3


# Create from YAML
kubectl apply -f deployment.yaml

Using YAML

Section titled “Using YAML”
deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80
        resources:
          limits:
            memory: "256Mi"
            cpu: "500m"
          requests:
            memory: "128Mi"
            cpu: "250m"

Deployment Strategies

Section titled “Deployment Strategies”

Rolling Update

Section titled “Rolling Update”
┌─────────────────────────────────────────────────────────────────────────────┐
│                      Rolling Update Strategy                                 │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                             │
│   Initial: nginx:1.20 (3 replicas)                                         │
│   ┌─────────┐  ┌─────────┐  ┌─────────┐                                   │
│   │1.20 │   │1.20 │   │1.20 │                                               │
│   └─────────┘  └─────────┘  └─────────┘                                   │
│                                                                             │
│   Step 1: Add 1 new pod with nginx:1.21                                   │
│   ┌─────────┐  ┌─────────┐  ┌─────────┐  ┌─────────┐                    │
│   │1.20 │   │1.20 │   │1.20 │   │1.21 │  ← new                         │
│   └─────────┘  └─────────┘  └─────────┘  └─────────┘                       │
│                                                                             │
│   Step 2: Remove 1 old pod                                                 │
│   ┌─────────┐  ┌─────────┐  ┌─────────┐                                   │
│   │1.20 │   │1.21 │   │1.21 │                                               │
│   └─────────┘  └─────────┘  └─────────┘                                   │
│                                                                             │
│   Continue until all pods are nginx:1.21                                   │
│                                                                             │
│   Default: maxSurge=1, maxUnavailable=0                                    │
│                                                                             │
└─────────────────────────────────────────────────────────────────────────────┘

Recreate

Section titled “Recreate”
spec:
  replicas: 3
  strategy:
    type: Recreate
┌─────────────────────────────────────────────────────────────────────────────┐
│                       Recreate Strategy                                     │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                             │
│   Initial: nginx:1.20 (3 replicas)                                         │
│   ┌─────────┐  ┌─────────┐  ┌─────────┐                                   │
│   │1.20 │   │1.20 │   │1.20 │                                               │
│   └─────────┘  └─────────┘  └─────────┘                                   │
│                                                                             │
│   Step 1: Kill all pods                                                    │
│   ┌─────────┐  ┌─────────┐  ┌─────────┐                                   │
│   │   X    │   │   X    │   │   X    │   (downtime)                      │
│   └─────────┘  └─────────┘  └─────────┘                                   │
│                                                                             │
│   Step 2: Create new pods                                                  │
│   ┌─────────┐  ┌─────────┐  ┌─────────┐                                   │
│   │1.21 │   │1.21 │   │1.21 │                                               │
│   └─────────┘  └─────────┘  └─────────┘                                   │
│                                                                             │
└─────────────────────────────────────────────────────────────────────────────┘

Managing Deployments

Section titled “Managing Deployments”
Terminal window
# Get deployments
kubectl get deployments


# Get deployment details
kubectl describe deployment nginx-deployment


# Scale deployment
kubectl scale deployment nginx-deployment --replicas=5


# Scale based on conditions
kubectl autoscale deployment nginx-deployment --min=2 --max=10 --cpu-percent=80


# Update image
kubectl set image deployment/nginx-deployment nginx=nginx:1.21


# View rollout status
kubectl rollout status deployment/nginx-deployment


# View rollout history
kubectl rollout history deployment/nginx-deployment

Rollback

Section titled “Rollback”
Terminal window
# Rollback to previous revision
kubectl rollout undo deployment/nginx-deployment


# Rollback to specific revision
kubectl rollout undo deployment/nginx-deployment --to-revision=2


# Check rollout status
kubectl rollout status deployment/nginx-deployment

Deployment Commands

Section titled “Deployment Commands”
Terminal window
# Apply deployment
kubectl apply -f deployment.yaml


# Delete deployment
kubectl delete deployment nginx-deployment


# Get deployment YAML
kubectl get deployment nginx -o yaml


# Watch rollout status
kubectl rollout status -w deployment/nginx-deployment


# Pause deployment
kubectl rollout pause deployment/nginx-deployment


# Resume deployment
kubectl rollout resume deployment/nginx-deployment


# Restart deployment
kubectl rollout restart deployment/nginx-deployment

Summary

Section titled “Summary”

In this chapter, you learned:

  • What Deployments are
  • Creating Deployments
  • Deployment strategies (Rolling Update, Recreate)
  • Managing Deployments (scale, update)
  • Rollback procedures

Next Steps

Section titled “Next Steps”